Melt spinning process



Jan. 14, 1964 J. J. KILIAN 3,118,012

MELT SPINNING PROCESS Filed March 8, 1962 2 Sheets-Sheet 1 INVENTOR JOSEPH JOHN KILIAN BY Ro w 23W ATTORNEY Jan. 14, 1964 J. J. KlLlAN MELT SPINNING PROCESS 2 Sheets-Sheet 2 Filed March 8, 1962 INVENTOR JOSEPH JOHN KILIAN ATTORNEY 3,118,012 MELT SPINNING PROCESS Joseph John Kilian, Galdand, Md., assignor to E. I. du Pont de Nemonrs and Company, Wilmington, Dei., a corporation of Delaware Filed Mar. 8, 1952, Ser. No. 182,990 13 Claims. (Cl. 264-176) This invention relates to the melt spinning of filaments from synthetic polymers. It relates particularly to a method of spinning such filaments at high productivity. This application is a continuation-in-part of my copending application Serial No. 810,362 filed May 1, 1959, and now abandoned.

In the preparation of fibers from fusible polymers, it is customary to force the molten polymer through the orifices of a spinneret into a region where the temperature is lower than the temperature of the molten polymer. In the cooler region, the molten polymer sets up into filaments sufficiently firm to be drawn away continuously by a yarn forwardly device. Conventionally, the molten polymer is spun through a spinneret having orifices spaced from each other by relatively large distances in order to keep newly formed filaments separated until they have congealed sufficiently to prevent their sticking together or coalescing. Productivity of yarn per spinneret under these conditions is low even at the highest practicable speeds of windup.

The large hole-to-hole spacing in conventional meltspinning spinnerets contrasts sharply with that used in spinning viscose, where the holes are spaced so closely together that a tow of several thousand filaments can be spun at a single position. Owing to smaller plant space, smaller investment in equipment, and lower expense of labor and up-keep, this high density of spinneret holes permits preparation of fibers at a much lower cost than is possible with conventional melt spinning.

A second disadvantage of known mel-spinning practices concerns the difiiculty of coupling the steps in yarn preparation. After a yarn is spun, drawing is generally necessary in order to raise the mechanical properties of the yarn to an acceptable level. However, yarn input to the drawing step usually proceeds at a rate necessarily different from the rate of yarn output from the spinning step. For example, it may be necessary to draw the yarn at a much lower rate than it is desirable to spin the yarn. Under such conditions it is most efiicient to interrupt the process of the yarn preparation, that is, to package the yarn temporarily after the spinning step for subsequent use in the drawing step. Even when it is possible to draw the yarn at a sufficiently rapid rate to allow its being used directly from the spinning step, the rate of yarn travel at the output from the drawing step often exceeds the capacity of currently available yarn handling equipment.

This difiiculty could be avoided by extruding the yarn slowly enough to allow the drawn yarn to be collected at a reasonable rate. But such an expedient would reduce the productivity of current spinning processes and would, therefore, be economically undesirable.

Accordingly, it is an object of this invention to provide a melt-spinning process for preparing yarns at high productivity. It is also an object to provide a melt-spinning process for preparing filaments having cross-sections which conform closely to the shape of the spinneret holes. Still another object is to spin yarns at high productivity at relatively low threadline velocity. Other objects will become apparent from the following specification and claims.

According to illustrative embodiments of this invention, a molten synthetic organic polymer is extruded through 100 to 2000 orifices arranged to form a pattern in which the centers of the orifices are positioned at the corners 3,118,012 Patented Jan. 14, 1964 of contiguous quadrilaterals formed by lines connecting the centers of adjacent orifices, with each side of each quadrilateral being between about 0.005 and about 0.125 inch in length, and all inside angles in each quadrilateral being at least 30. The polymer is extruded at a weight rate (W) of 4 to 40 g./min./cm. and preferably from 10 to 30 g./min./cm. of elfective spinneret face area within the quadrilaterals. Effective spinning under these conditions, although impossible under previously known procedures, is readily accomplished in accordance with the present invention by directly a stream of gaseous quenching medium against each filament at a velocity of at least 0.6 W +l50 feet per minute within 1 inch of the spinneret face at an angle between 45 below and 45 above the horizontal, to cool the extruded filaments at least about 15 C. and preferably at least 25 C. below the melting point of the polymer prior to a point 2 inches below the spinneret, while maintaining the extruded filaments being under a tension of at least 0.003 gram per denier immediately below the spinneret.

By the expression effective spinneret face area is meant the area within a quadrilateral defined by four straight lines between the centers of four adjacent orifices. Thus, if the orifices are arranged in a square pattern, the effective spinneret area is the square of the center-t0- center spacing of the orifices. When the orifices are arranged in staggered rows, the effective area is a parallelogram with sides corresponding to center-to-center distances in a row and center-to-center spacings between orifices in different rows. The manner of determining this value for other arrangements will be obvious.

It has been found that the minimum velocity of gaseous quenching medium necessary at the threadline within 1 inch of the spinneret face may be calculated from the expression:

where V is the linear velocity in feet per minute of the gas impinging on the filaments and W is the weight extrusion rate or throughput of polymer in grams/minute/cm. of effective spinneret face area. This expression is valid for a quenching medium having a temperature of about 20 C. Since W has a value of at least 4 g./min./cm. the minimum velocity of the quench medium useful in pthe present invention is 0.6(4) ll50, or approximately feet/ minute.

The quench velocity (V which is satisfactory at a given extrusion rate and quench medium temperature (T in degrees Kelvin) may be corrected to the required velocity (V at a different temperature of the quenching medium (T in degrees Kelvin) by the expression:

The temperature correction is so slight that the process can be operated within a range of 20i7 with a variation of no more than 12.5% in the quenching medium velocity.

Preferably, the temperature of the quenching medium will be between about 15 and 40 C. The use of a cooler medium adds undue cost to the process. The use of hot mediums, e.g., C. and above is undesirable because the velocity of quench must be increased to an extent which makes good spinning difficult, as the filaments may be blown together or the threadline broken.

The quenching medium is preferably a gas or vapor of a liquid having a boiling point at atmospheric pressure below about 10 C. Vapors of higher boiling liquids can cause process difficulties due to partial condensation of the vapor, which can interfere with the quenching system and cause non-uniformities in the yarn. The preferred class of quenching medium is illustrated by air, nitrogen, helium, or carbon dioxide.

It is found that the as-spun denier of the filaments prior to drawing has no practical eiTect on the quench velocities required at a given extrusion rate. This is shown by runs 24 to 28 of Table 2 where the temperature of the filaments varies only as the denier is changed from 2.8 to 22.6. In general, filaments having as-spun deniers in the range of /2 to 100 can be spun by the process of this invention using the previously stated quenching conditions.

Other spinning process variables, such as orifice diameter and spinning speed, do not elfect the minimum quench velocity needed at a specified extrusion rate.

The amount of quenching used in accordance with this invention is unlike anything known to the prior art. A typical prior art disclosure is that of U.S. Patent No. 2,821,749, issued February 4, 1958, to I. E. Spohn et al., which relates to the use of a very gentle flow of air at a die face, during extrusion of filaments, in order to avoid clogging of the spinneret holes. Although the air is supplied at a jet velocity of 100 feet per minute through a small jet located about 2.8 inches from the die, nevertheless, due to the expansion of the air past the jet, the linear velocity of the air decreases to less than feet/ minute by the time it reaches the filaments at the die face. The patent also specifically discloses operation with air pressures as high as 7 and as low as 0.5 pound per square inch gauge and jet clearances of between 0.005 inch and 0.030 inch. The maximum velocity would be obtained from the higher pressure and larger jet clearance. I. have determined that the maximum velocity of the air at the die face under these conditions is less than feet per minute.

In the drawings, which illustrate specific embodiments of the invention,

FEGURE 1 illustrates schematically the process of the invention.

FIGURE 2 shows a spinneret hole pattern suitable for use in the process.

FIGURES 3 and 4 illustrate a particular apparatus embodiment of the process.

In FIGURE 1, the invention is shown in its simplest form. Molten polymer is extruded through orifices 1 in spinneret 2, the orifices being arranged in a plurality of parallel straight rows 3 forming a pattern 4 bounded by perimeter 5. A strong current of quenching gas from nozzle 6 impinges upon the newly formed filaments 7 as they emerge from the spinneret. The bundle of quenched filaments is removed from the quenching region under tension by yarn-forwarding roll 8, which may be a windup or a guide roll for conveying the yarn to the next processing step, which may be a drawing step. The pattern 4 consists of closely spaced multiple rows of holes 1. The position of the quenching nozzle 6 may be specified by d and h which are, respectively, the vertical and horizontal distances of the nozzle from the center of the pattern. The orientation of the nozzle is specified by the angle 0, measured from the h'on'zontal, which is the angle the quenching stream makes with the horizontal. Ordinarily, it is advantageous if the quenching stream is imposed perpendicular to the rows of holes 3 in the pattern 4. However, the quenching stream may be imposed at an angle to the rows of holes. The angle is used to designate this angle. The invention is intended to include such a quenching arrangement, so long as the major component of the quenching stream is perpendicular to the rows of holes, that is, so long as p is less than The distance s between the rows of holes 3 is no more than about 0.125 inch. The pattern 4 need not be rectangular, but may, for example, consist of rows of holes arranged on the circumferences of a plurality of closely spaced concentric circles as shown in FIGURE 2. For this arrangement of the holes, the quenching stream is preferably radially inward as at S, or radially outward as at B, and the spacing s between circumferences 22 and 23 is less than about 0.125 inch.

FIGURE 3 shows one embodiment of the apparatus in greater detail. Molten polymer is forced through sand pack 12 and then through channels 13 leading to holes 14 on the face of the spinneret 15'. Band heater 16 may be used to control the temperature of the spinneret independently of the flow of polymer, which heats the spinneret, and quenching gas, which cools it. The filaments 17 emerging from the holes are immediately quenched by a strong how of gas from primary nozzles 13, directed across the bundle of filaments and parallel to the face of the spinneret. In this embodiment, after passing through the initial quenching zone, the filaments enter a secondary cooling zone in which they are subjected .to a flow of gas from nozzles 19. This flow of gas further cools the filaments, and also is so imposed as to counteract the deflection due to the action of gas from nozzles 28. Thereafter the filaments pass to a windup or yarn-forwarding device.

Gas supplied to nozzles 18 and 19 passes over flow chopper vanes 20-, which serve to distribute the gas evenly. The nozzles may also be covered by screens 21 in order to make the flow of gas more homogeneous.

FIGURE 4 shows in plan the face of one type of spinneret suitable for use with a circular 5" pack. The working area ABCDEFGH is divided into two parts for more effective quenching. The two areas ABGI-I and CDEF each contain 810 holes arranged in rows with a center-to-center spacing of 0.060 inch between rows and between holes. *In each area there are 14 rows of holes perpendicular to the direction of the quenching gas. The position of the quenching nozzles is shown as 18 and 19. Example 3 below describes in detail the operation of this embodiment under a particular set of conditions.

It is a surprising fact, unrecognized 'by the art, that multiple rows of holes at close spacing may be employed in conjunction with a strong current of quenching gas, imposed at the spinneret, in the melt spinning of synthetic polymers.

In conventional spinning practice it is not possible to spin a large number of holes at one position. In the case of 3-denier-per-filament polyethylene terephthalate a maximum of about 250 holes can be spun from a 5-inch pack, while in the case of nylon only about holes can be spun. One diificulty which arises when it is attempted to spin more holes is that a stronger current of air must blow across the chimney. This causes a more severe deflection of the newly formed filaments and leads to yarn which is less uniform. It also causes filaments to move about more, leading to stuck filaments. The fact that the filaments are closer together aggravates the situation and increases the number of stuck filaments still further. Consequently, conventional spinning is very limited in the number of holes which can be spun per position. With the present invention at least 2000-3 denier per filament polyethylene terephthalate or nylon filaments may be spun from a 5-inch pack.

It is a feature of the present invention that the number of holes in the spinneret and the amount of quenching air are simultaneously increased without resulting in stuck filaments. This is achieved by imposing the quenching stream at, or very near, the face of the spinneret. The benefit derived from this mode of operation is that the filaments are quickly cooled to a temperature at which their viscosity is sufiiciently great to support a much greater tension. Owing to the tension which is imposed upon the threadline at the windup, large deflections of the filaments do not occur. In addition, the length of the critical region where the filaments are tacky is drastically reduced. In fact, when the temperature of the threadline at a point two inches below the spinneret is reduced to below about 15 q C. and preferably below 25 C. below the melting temperature, no stuck filaments result.

Thus, in comparison with conventional melt spinning, the present process allows a much larger number of filaments to be spun per spinneret, or alternatively, it allows the same number of filaments to be spun for a much smaller spinneret. Under suitable conditions, it allows a yarn to be spun at a speed which is low enough to allow it to be drawn directly in a coupled process. Alternatively, it allows a yarn to be spun with sufiiciently high as-spun properties to render a drawing step unnecessary. In either case the product may be made spontaneously crimpable if desired, by imposing a strong asymmetric quenching stream having a velocity strong enough to impart a tension of at least about 19 mg./ denier to the threadline. This spontaneously crimpable product has an unusual spiral crimp, and leads to fabrics having greatly improved cover, when compared with fabrics prepared from stutterbox crimped fiber.

Examples 1 and 2 shows that for the polymers polyethylene terephthalate and polyhexamethylene adipamide the invention may be operated under a wide range of conditions, provided the filaments are quenched enough to bring the threadline within two inches of the spinneret to a temperature below 15 C. below and preferably below 25 C. below the melting point of the polymer. Relative viscosities are determined at 25 C.

EXAMPLE 1 Polyethylene terephthalate chip having a relative viscosity of 35 in trichlorophenol/phenol (70/100) and a melting point of 245 C. is vacuum dried for 16 hours at 105 C. The polymer is charged into the hopper of a grid melt spinning unit and blanketed with nitrogen. The temperature of of the grid melt unit is maintained at 285 C. The molten polymer is then pumped through a sand pack filter and extruded vertically downward through a spinneret containing 48 holes in a 4 x 12 rectangular array. The diameter of each hole is 0.009 inch, and the center-towenter spacing is 0.050 inch. Thus, the effective spinneret face area is 0.016 cm. The capillary leading to each hole is 0.030 inch long, and it in turn is fed through a larger capillary having a diameter of 0.040 inch and a length of 0.35 inch. The spinneret temperature is 275 C.

The newly formed filaments are uniformly quenched with air directed slightly upward toward the center of the spinneret pattern from a Vs x 2" slot situated 7 horizontally distant and vertically downward from the face of the spinneret. The long dimension of the slot is parallel to the ground and to the long dimension of the spinneret pattern. Quench air is controlled by means of a Fischer and Porter Flowrator (Type B27250/70) with a pressure reducer and pressure gauge upstream of the Flowrator. Air velocity is measured at the spinneret by means of a Weston or Alnor anemometer.

The temperature of the quenched filaments is measured at a point 2" below the face of the spinneret. This measurement is made by a comparison technique, using an infrared vacuum thermocouple as a detector. A strip heater is covered :with polyethylene terephthalate film and placed /2 from the filament bundle as a background. A concave mirror placed on the opposite side of the bundle focuses infrared radiation on the detector. As the temperature of the background is raised, the mirror is focused alternately on the background and on the back ground and filament bundle together. When the temperature of the background is the same as the temperature of the filament bundle, there will be no change in the output from the detector when the focus is changed. At this point the temperature of the background is determined by thermocouple.

The temperature of the filaments is measured for various throughputs, quench velocities, and windup speeds. The data are presented in Table l. The temperature is observed to vary with the logarithum of the quench velocity.

The tension of the threadline as measured with a tensiometer 5 feet below the spinneret for the following spins varied from 3 to 40 milligram (mg) per denier at 100 QUENCH SPUN POLYETHYLENE TEREPHTHALATT FILAlVIENT Through- Denier Air Windup Filament Run put (g./ per Velocity Speed, Temp.,

Elm/0111. Filament (ft./min.) y.p.m. C.

13. 6 10. 4 910 139 13. 6 10. 4 540 100 189 13. 6 10. 4 380 100 211 17. 1 27. 1 1, 900 100 20. 5 32. 4 540 100 202 20. 5 32. 4 910 100 176 20. 5 32. 4 1, 300 100 162 20. 5 32. 4 1, 900 100 157 24. 1 38. 2 910 100 103 24. 1 38. 2 l, 300 100 174 24. l 38. 2 1, 700 100 165 24. 1 38. 2 2, 050 100 163 17. 1 27. l 540 100 198 17. 1 6. 8 540 400 195 17. 1 4. 5 540 600 187 17. 1 3. 4 540 800 17. 1 2. 7 540 1,000 182 The above polymer was also extruded from spinnerets having 300 holes spaced 0.018 inch apart on centers, and from spinnerets having 96 holes spaced .030 inch apart using a similar quench.

Operating the above procedure without a quenching fluid at a throughput of from 8.7 to 24 g./min./cm. produced filament temperatures greater than 250 C. and in all cases the filaments were fused together.

EXAMPLE 2 Polyhexamethylene adipamide (nylon) having a relative viscosity of 35 in 90% formic acid and a melting point of 255 C. is dried, melted and spun according to the same procedure as that used in Example 1. Threadline temperature is measured in the same way, with the exception that the strip heater is covered with a nylon film to serve as the background. The data are presented in Table 2.

The tensions on the threadline vary from 3 to about 60 mg./denier at 100 y.p.m. In conventional spinning of this polymer at similar speeds and temperature tensions in the range of 1 to 3 mg./ denier are observed.

Operating the above procedure without a quenching fluid at a throughput of from 8.7 to 24 g./min./cm. produced filament temperatures greater than 250 C. and in all cases the filaments were fused together.

Table 2 FILAMENT TEMPERATURE MEASUREMENT OF JET QUENCH SPUN 6-6 NYLON Through- Denier Air Windup Filament Run put (g./ per Velocity Speed, Temp.,

min/cm?) Filament (ft./1nin.) y.p.m. C.

EXAMPLE 3 Polyethylene terephthalate chip having a relative viscosity of 21.7 in a mixture of tetrachloroethane/phenol (66/100) is spun from the apparatus shown in FIGURES 3 and 4. The spinneret holes are 0.007 inch in diameter and have capillaries 0.012 inch in length. Individual counter-bores 0.040 inch in diameter and 0.30 mch in length feed the capillaries. The effective spinneret face area is 0.0232 cm. The polymer temperature 18 maintained at 290 C. The volume of room temperature air delivered from each primary quench nozzle is 60 standard cubic feet per minute (s.c.f.m.) flowing at an average velocity of 1525 feet per minute. The volume of air delivered from each of the secondary nozzles is 18 s.c .i.m., flowing at an average velocity of 450 feet per minute. Polymer is extruded at a rate of 0.45 gram per minute per hole (19.4 g./min./cm. and is wound up as a 17.7 denier per filament undrawn yarn at 250 yards per nunute. Since there are 1620 holes in the spinneret, this cor responds to a productivity of 96 pounds per hour of 28,700 denier yarn for the entire spinneret. The as-spun yarn has a tenacity of 0.76 g.p.d. and an elongation to break of 406%. The yarn is drawn to 4.6 times its original length (4.6X). Boiling the yarn in water to relax it causes the development of 8 helical crimps per inch. The drawn and relaxed product (4.6 d.p.f.) has a tenacity of 2.9 grams per denier, an elongation of 33%, and an initial modulus of 26.4 grams per denier.

Under appropriate spinning conditions, the rapid quenching which is achieved in the present invention leads to filaments having high as-spun properties. Molecular orientation is induced both during flow of the molten polymer through the channel leading to the spinneret hole and by stretching as the filament is drawn away under relatively high tension. By sufficiently rapid quenching, this orientation may be frozen into the polymer structure, and a stronger, stiffer fibre results. When the quenching is carried out asymmetrically, the orientation is preserved to a greater extent on the quenched than on the unquenched side of the filament. A self-crimpable yarn results. These elfects are illustrated in Examples 4, 5, and 11.

EXAMPE 4 Polyhexamethylene adipamide having a relative viscosity of 41 in 90% formic acid is charged into a grid melt spinning unit at 289 C. The polymer is extruded through a spinneret whose holes are set at a 0.050 inch spacing and arranged in a 4 x 12 rectangular pattern. T he spinneret temperature is adjusted to 260 C. by means of an auxiliary heater. The polymer is extruded at a rate of 11.0 grams per minute (14.2 g./min./crn. and wound up at 95 yards per minute. Quenching air is delivered from a Bunsen burner wing tip at a velocity at the spinneret face of 11,000 -ft./rnin. The wing tip is oriented so that its long dimension is parallel to the face of the spinneret and to the long dimension of the hole pattern. It is situated one inch below and 2 /2 inches horizontally distant from the center of the spinneret, and is directed upward at an angle of 17 with the horizontal. The tension on the filament bundle is 22 to 24 grams (19 nag/denier). The properties of the yarn after boil-off are denier per filament 24; tenacity 0.9 gram per denier; elongation 145%; initial modulus 5.4 grams per denier; 6 to 7 crimps per inch; crimp elongation 185%.

Yarn of this character is directly suitable for use in carpets. In this end use low toughness (:work to break) is considered advantageous and the carpets do not fuzz or pill. A similar denier as-spun fiber prepared by extruding the above polymer with a conventional chimney quench has a tenacity of 0.8 g.p.d. and an elongation of 450%. Carpets prepared from it fuzz and pill badly.

EXAMPLE Polyethylene terephthalate having a relative viscosity of 34 in trichlorophenol/phenol (7/10) is charged into a grid melt unit at a temperature of 285 C. and extruded through a spinneret at a temperature of 270 C. The spinneret contains 100 holes at 0.050 inch center-to-center spacing arranged in a rectangular 5 x 20 pattern. Polymer is extruded at 10.0 grams per minute (6.2 g./min./cm.

and Wound up at 1000 yards per minute. Quenching air is directed from a 1" x 5" slot to deliver air at 750 feet per minute at the spinneret. The slot is oriented with its long dimension parallel to the face of the spinneret and to the long dimension of the hole pattern. It is situated one inch vertically downward from the face of the spinneret and two inches horizontally distant from the filament bundle. The quenching stream is directed upward at an angle of 30 from the horizontal. As-spun properties are denier per filament 1.0; tenacity 2.7 grams per denier; elongation 200%; initial modulus 25 grams per denier. The yarn is drawn 2X in C. Water and then has the following properties: denier per filament 0.48; tenacity 5.2 grams per denier; elongation 23%; initial modulus 88 grams per denier. By the process of this invention it is commercially feasible to produce fine filaments having a denier from 0.1 to 1.0. This has not been possible heretofore.

The as-spun yarn obtained in Example 5, after being boiled off taut, has properties adequate for many end uses. If still higher properties are desired, it will be noted that the as-spun yarn may be drawn to a tenacity of 5 grams per denier in a coupled process at a speed of 2000 yards per minute, which is well Within the capacity of conventional equipment.

An advantage of the present invention is that polymers which would ordinarily be considered unspinnable because of their relatively low melt viscosities can be spun without difficulty. This comes about because the temperature of the extruded polymer is quickly reduced and its viscosity thereby raised to a value at which the filament resists threadline breakage due to the force of surface tension. This circumstance can be put to use in avoiding filtration ditficulties. Thus, at the high throughputs achieved in the present invention sufficiently rapid filtration of the polymer melt sometimes presents a problem. For polymers whose fiber properties are not highly sensitive to changes in molecular weight, the problem may be avoided by lowering the molecular weight of the polymer, with a consequent reduction in viscosity and more rapid filtration.

The following example illustrates the spinning of a polymer not spinnable by conventional means.

EXAMPLE 6 A sample of polyhexamethylene adipamide having a relative viscosity of 16.5 to 8.4% concentration in m-cresol is spun from a grid melt unit in which the melt is maintained at 270 C. through a spinneret maintained at 250 C. The spinneret contains forty 0.009 inch diameter orifices set at 0.050 inch spacing in a 4 x 10 rectangular array. Quenching air is directed toward the center of the hole pattern from a m" x 2" slot situated 2 inches horizontally distant from the filaments and one inch vertically downward from the face of the spinneret. The long dimension of the jet slot is parallel to the long dimension of the hole pattern. At a polymer throughput of 0.0815 gram/minute/hole (5 g./min./cm. and an air velocity at the spinneret of 1500 ft./min., the yarn is Wound up at yds./minute. After being drawn about 4 /2X on a hot plate at 200 (3., followed by a /2 hour boil-off, the yarn has the following properties: tenacity 5.1 g.p.d.; elongation 31%; initial modulus 22%; denier per filament 2.2. This polymer could not be spun by conventional commercial spinning methods.

Using a similar technique as above, poly(ethylene terephthalate) with a relative viscosity of 10 is satisfactorily spun.

Examples 7, 8, and 9 illustrate the operation of the process with a variety of polymers.

The expression relative viscosity as used herein signifies a ratio of the flow time in a viscosimeter of a polymer solution containing 8.2% 10.2% by weight of polymer in a solvent relative to the flow time of the solvent by itself.

The lowest molecular weight poly(hexamethy-lene adipamide) that is commercially spun and drawn at the present time as single component filaments is that which corresponds to a relative viscosity of 27 but, for the production of first-class yarn, relative viscosities of 36 and higher are now used. The commercially acceptable molecular weight levels of other polyamides will vary with the specific polymer, but in general they will be of a magnitude comparable tothe above. In contrast, using the process of this invention poly(hexamethylene adipamide) and similar polyamides having a viscosity in the range of 12 to and higher can readily be spun.

Poly(ethylene terephthalate) of relative viscosity 22 or greater must be used in conventional procedures for commercial spinning and drawing but relative viscosities of -33 are currently used in commerce to avoid denier non-uniformities, spinning and drawing breaks that are prevalent when using the lower molecular weight. Using the process of this invention, such polyesters with a viscosity of 9 or higher can readily be spun at commercially feasible rates.

EXAMPLE 7 A sample of Lustrex-15 polystyrene flake having a molecular weight of to 40,000 and an inherent viscosity of 0.66 at a concentration of 0.5% of benzene, is dried in a vacuum oven at 100 C. and 1 mm. pressure. The polymer is spun from a melt pool at a temperature of 240 C. through a spinneret containing 100 holes arranged in a 10 x 10 square matrix at 0.050 inch spacing. The orifice diameter is 0.009 inch. The spinneret temperature is varied between 180 and 220 C. The quenching air is directed upwardly at an angle of 18 /2" with the horizontal. The quenching device is a tube having an inside diameter of /8 whose orifice is situated 1%" below the spinneret and 2 from the threadline. The rate of flow of quenching air is varied between 1.2 and 5.0 s.c.f.m. Typical operable spinning conditions are shown in Table 3. The quench velocities of the first four items in Table 3 are 1600, 4700, 8000, and 14,000 feet/minute, respectively.

Table 3 Windup spinneret Flow of Quenching gJminJeru. Speed Tension Temp.

Air (s.c.f.m.) (yds/min.) (gms) C.)

Tensions on the spinning threadline which are recorded in this table are exceptionally high even for the present process. The sample spun at a delivery of 8.1 grams/minute/cm. and at a quench rate of 5.0 s.c.f.m. has the following properties: tenacity 0:84 g.p.d.; elongation 4%; initial modulus 30 g.p.d.; denier per filament 30. The sample spun at a delivery of 4.7 grarns/minute/cm. has the following properties: tenactity 0.94 g.p.d.; elongation 27%; denier per filament 7.7.

EMMPLE 8 Polyethylene having a density of 0.93 and a melt index of 12 is melt extruded at 290 C. through the spinneret described in Example 7. The throughput is 0.093 gram/ minute/hole (5.8 g./min./cm. The jet geometry is the same as that described in Example 7. Typical operable spinning conditions are shown in Table 4. The

quench velocities range from 2100 to 15,000 feet/ minute. 75

The yarn quenched at the spinneret face with an air velocity of 15,000 ft./min. (5.9 s.c.f.m.) had the following properties: tenacity 0.27 g.p.d.; elongation 240%; initial modulus 1.93 g.p.d.; denier 63.0.

EXAMPLE 9 An elastomeric copolyester is prepared from ethylene glycol, polytetramethylene oxide glycol having a molecular weight of 1560, and terephthalic acid. The weight ratio of ethylene terephthalate units to polytetramethylene oxide terephthalate units is 2 to 3. The polymer has an inherent viscosity of 1.05 in tetrachloroethane/phenol (66/100). It is stabilized with /2% of an antioxidant such as bis(2-methyl-4,6 dihydroxyphenyl)methane. The polymer is spun from a grid melt unit maintained at a temperature of 225-245 C. The spinneret temperature is 218 C. The quenching conditions and the spinneret used are the same as those of Example 7. The polymer is spun at a delivery rate of 0.075 gram/minute/hole (4.7 g./min./cm. is quenched with a flow of air at the rate of 1.2 s.c.f.m, and is wound up at 35 yds./ minute. In order to minimize the tendency of the filaments to stick together, tale is applied to the spinning threadline by means of a flock gun. Properties of the spun yarn are as follows: tenacity 0.15 g.p.d.; elongation 1016%; initial modulus 0.33 g.p.d.; denier per filament 38.2.

EXAMPLE 10 Semi-dull polyethylene terephthalate having a relative viscosity of 34 is spun from a grid melt unit through a spinneret having one-hundred 0.009 inch diameter holes arranged in 20 x 5 rectangular array on a 0.050 inch spacing. The threadline is quenched by hot air emerging from a 1%. inch x 5 inch slot situated two inches horizontally distant from the center of the pattern and one inch vertically downward from the face or the spinneret. The air is directed upward at an angle of 30 with the horizontal. The slot is oriented such that its long dimension is parallel to the long dimension of the spinneret pattern. The velocity of the quenching air at the spinneret is 825 ft./min. Maximum windup rates achieved at two different throughputs for various temperatures of the quenching air are shown in Table 5.

This example illustrates a preferred process of this invention.

Polyethylene terephthalate chip having a relative viscosity of 31.2 as measured in a mixture of tetrachloromethane/phenol (66/100) is melted and the melt (at about 290 C.) is extruded (49-51 pounds of polymer per hour) through a spinneret maintained at 278 C.- 300 C. by an auxiliary electric heater around the circumference of the spinneret. The spinneret comprises 900 holes (each 0.007 in diameter) arranged on six concentric circles whose radii differ by 0.052 inch each, the smallest circle of which has a radius of 1.437 inches. The holes are located on radii of the circle. Adjacent radii are spaced 112 apart and contain holes spaced on alternate circles so that a staggered pattern is obtained. Thus, the center-to-center spacings in a row (circle) vary from about 0.060 inch in the inner circle to about 0.071 inch in the outer circle. The average effective spinneret face area per hole (taken between rows 3 and 4) is 2.2 l cm. to a give a throughput of 18.7l9.5 g./min./cm. The extruded filaments are uniformly quenched with room temperature air from a quenching nozzle surrounding the circle of filaments comprising a slot 1 inch high located on the inside surface of a cylinder chamber having an inside diameter of 4% inches. The top of the slot is spaced inch below the spinneret face by a ring of aluminum foil and heavy asbestos cloth. The filaments are wound up at various speeds and the as-spun filaments are combined to a tow of convenient size and drawn through a hot water bath or spray (about 95 C.) to an extent so as to give about elongation at the break of the as-drawn yarn. The as-drawn filaments develop a high degree of helical crimp immediately upon release of the drawing tension. The fibers are relaxed at IOU-200 C. (preferably 140 C.) for 2 to 20 minutes. The effect of different amounts of quench is shown in Table 6. The velocities of the quench at the threadline for the four items are 2200, 440, 1770 and 1770 feet/minute, respectively. Item a has 11 crimps per inch of crimped length.

The crimp index is used as a measure of the extent of crimp and is determined from the length of a sample of crimped tow hanging under an added load of 0.1 g.p.d. for a period of 2 seconds (length A) and the length of that tow hanging under no added weight after it has relaxed for 15 seconds from the first extension (length B) where crimp index:

Items a, c, and d in Table 6 are very useful in staple form as filling for pillows.

When the above spins were attempted to be repeated with the substitution of a conventional chimney (with an opening 4.75" wide and 39" long, the top of which is located 2" below the face of the spinneret) quenching system with a very high air flow (400 c.f.m.), they were inoperative at throughput levels of 4.0 g./min./cm. and

Spiiznerei block temperature.(temperature of the polymer melt before passage through the spinneret) For purposes of making crimped filaments, a higher temperature of the melt is usually required in the case of copolyesters than is normally used in conventional spinning.

Spilmeret temperazure.The crimp index is reduced as the s inneret temperature is raised.

Hole spacir zgs.The hole spacings of this invention, i.e., where the centers of adjacent orifices are less than 0.125 inch apart are satisfactory.

Hole size or orifice size.in general, larger holes give a higher crimp index level at the crimp index levels of 30 and higher. Thus, a 0.014 inch diameter orifice is preferred in the preparation of products such as shown in Table 6.

Air quench-As the air quench is increased, the crimp index is increased. A radially directed inward quenching stream at 0 to horizontal is preferred as producing substantially more uniform products.

Polymer thr0ughput.-As the amount of polymer going through an orifice in a given time increases, the crimp index of the final yarn decreases.

Draw ratio.This should be considered as the total orientation obtained in combination by spinning and drawing as the spinning conditions will control the absolute draw ratio. However, as the draw ratio is decreased, below that required to give a break elongation (on unrelaxed drawn yarn) of less than about 17%, the crimp index decreases rapidly. Preferably, to gain maximum crimp index, the yarn should be drawn to give a 10% elongation at the break of the unrelaxed drawn yarn.

Drawing c0ml1'ti0ns.Drawing in a bath or spray of hot water is preferred. Drawing over a hot pin (e.g., 80- 90 C.) lowers the crimp index.

Filament denier.As the denier is increased, the crimp index is reduced.

EXAMPLE 12 Polypropylene with a melt index of 0.7 (ASTM D 123 8-571) is extruded at a rate of 5.2 g./min./cm. from a pool of the molten polymer at 280290 C. through a spinneret maintained at 260 C. and the yarn wound up at 183 y.p.m. The spinneret contains 38 holes of 0.009 inch in diameter in 4 rows, the holes being arranged in a square pattern 0.050 inch apart in each direction from adjacent holes. A quenching nozzle with a width of 1.25 inches and a height of 2 inches is placed with its long dimension vertical, /2 inch below the face of the spinneret and 1 inch horizontally distant from the outer row of filaments. Room temperature air is then fed through this nozzle at a rate of 21 s.c.f.m. (a velocity of 1800 feet per higher. Air velocity (calculated average) was 311 linear minute at the threadline) which affords a tension on the ft,/min threadline of 28 mg. per denier.

T able 6 Quenching Conditions Relaxed Fiber Properties ind- Item up Spin Tenacity,

Speed, neret cu. ft. Draw Crimp g.p.d./ Initial y.p.rn Temp., air/lb. Ratio Index Elonga- Modulus d.p.f.

C. polymer tion,

Percent The as-spun yarn (4.7 d.p.f.) is found to have a surprisingly low crystallinity (about 0.6 of the level obtained from this polymer by conventional quenching methods), and after relaxation (boiling in Water), has a tenacity of 1.9 g.p.d., a break elongation of 360%, an initial modulus of 7, and has 10-15 crimps per inch.

The as-spun yarn is then drawn 1.67X in 96 C. water and then further drawn 1.91X over a metal plate heated to 112 C. to give a total draw of 32X. The drawn yarn, after relaxing by boiling in water, has a tenacity of 5.9

g.p.d., an elongation of 30% at the break, and an initial modulus of 29 g.p.d. The filaments are straight and uncrimped.

EXAMPLE 13 Polyethylene terephthalate (relative viscosity of 32) is extruded from a melt at 290 C. through a spinneret having 126 holes of 0.007 inch diameter arranged in a 7 x 18 rectangular pattern of holes at a center-to-center hole distance of 0.050 inch. The extrusion rate is 10.6 g./min./cm. The threadline is quenched by 1" x 2" nozzle, the center of which is located 1" below the spinneret face and 1 /2" horizontally distant from the center of the threadline. The nozzle is tilted upward so that the quenching stream is at an angle of 20 with the horizontal. The 1.7 denier per filament quench filaments are wound up at a speed of 1000 yards per minute. Good spinning is obtained using 35 C. air at a velocity of 230 feet per minute at the threadline. This velocity is slightly above the minimum required. The temperature of the quench air is then raised by passing the above 35 air supply at the above constant flow rate through a heater. Excellent spinning is obtained at quench temperatures of 58 98, 126, 154 and 169 C. The calculated quench velocities are 248, 280, 298, 316 and 330 feet/minute, respectively, for these temperatures.

The invention is applicable to any melt spinnable synthetic organic polymer including, for example, polyamides, polyesters, polyhydrocarbons such as polyethylene and polypropylene, polyurethanes, polyureas, vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, and copolymers thereof, acrylic polymers such as polyacrylonitrile when sufficiently plasticized to render it fusible, copolymers of acrylonitrile, halogenated hydrocarbons such as polychlorotrifluoroethylene, polyacetals, polyanhydrides, polyoxymethylenes, polyformals, polyethers, polythioethers, polysulfides, polythioesters, polysulfones, polythioureas, polythioamides, polysulfonamides, polyimides, and polytriazoles. Copolymers of all sorts are usable.

Because of their commercial availability, ease of processing and excellent properties, the condensation polymers and copolymers, e.g., polyamides, polysulfonamides and polyesters and particularly those that can be readily melt spun are preferred for application in this method. Suitable polymers can be found, for instance, among the fiber-forming polyamides and polyesters which are described, e.g., in US. Patent Nos. 2,071,250, 2,071,253, 2,130,523, 2,130,948, 2,190,770, and 2,465,319. The preferred group of polyamides comprises such polymers as poly(hexarnethyleneadipamide), polyhexamethylene senacamide), poly(epsiloncaproarnide), and the copolymers thereof. Among the polyesters that may be mentioned, besides poly(ethylene terephthalate), are the corresponding copolymers containing sebacic acid, adipic acid, isophthalic acid as well as the polyesters containing recurring units derived from glycols with more than two carbons in the chain, e.g., diethylene glycol, butylene glycol, decamethylene glycol and trans-bis-1,4(hydroxymethyl) cyclohexane.

The spinneret may have a flat face or a face so sculptured as to facilitate cooling of the vicinity of the orifices, either symmetrically or asymmetrically. For instance, the face of the spinneret may have flanges or grooves in the direction of quenching in order to conduct the flow of gas in a more uniform fashion. If desired, the holes may also be placed on individual nipples in order to facilitate rapid cooling.

The spinneret orifices may be round, to produce filaments having circular cross-sections, or may be non-round to produce filaments having arbitrary cross-sections as illustrated by the following examples:

EXAMPLE 14 Polyhexarnethylene adipamide having a relative viscosity of 39 is spun from a melt at a temperature of 288 C. through a spinneret at a temperature of 260 C. This spinneret contains 35 holes arranged in a 7 x 5 staggered, rectangular pattern, the distance of each hole from its nearest neighbors being 0.050 inch (centert-o-center). Each hole consists of three slots, 0.010 inch long and 0.003 inch wide, set radially at angles of 120 around a 0.007 inch circular center hole. The polymer is extruded at a rate of 0.3 gram per minute per hole (18.6 g./min./cm. The quenching medium is delivered through a cylindrical sintered bronze surface which is 2 inches in inside diameter and 1% inches long, and is situated coaxially with the yarn bundle with its top inch below the face of the spinneret. The quenching medium is F. air, delivered at 14 s.c.f.m. (standard cubic feet per minute) radially inward toward the yarn bundle. The yarn is drawn over an 8-inch hot plate. Table 7 gives physical properties of the yarn for two sets of operating conditions.

Table 7 Speeds (y.p.m.) Denier Draw per Temp, Fila- T E Mi Feed Draw C. ment Roll Roll T=tenacity (grams per denier). E= elongation (percent). Mt=initial modulus (grams per denier).

EXAMPLE 15 Polyethylene terephthalate having a relative viscosity of 35 and containing 0.3% TiO is extruded from a melt at 286 C. through a spinneret maintained at 274 C. The spinneret comprises 33 holes arranged in 5 rows so that the center of each orifice is 0.07 inch from the center of the adjacent orifices. The orifices consist of 6 rectangular slots, each 0.003 inch by 0.012 inch long, radiating from a common center point at 60 angles to com prise a six-membered star. Polymer passing through each orifice at the rate of 0.43 gram per minute (13.6 g./min./cm. is quenched by F. air from a circular quenching apparatus directed inward at the threadline at a value of 5.5 s.c.f.m. (70 F. 1 atmosphere, absolute). The quenching apparatus consists of a porous bronze tube of 1.75 inches ID. and 1.5 inches long located about 0.25 inch below the face of the spinneret. The yarn is wound up at 1230 y.p.m. and is 115 denier as spun.

The as-spun yarn is drawn over a hot pin at 110 C. at 100 y.p.m. to give 70 denier yarn (1.65X draw ratio) with the following properties: tenacity 3.58 g.p.d.; elongation 66%; and modulus 51 g.p.d. The drawn yarn was then made into a taffeta fabric of plain weave with a finished construction of 128 x having a finished weight of 2.10 ounces per square yard, a bulk of 2.56 cm. gram, and a coefiicient of friction (fabric on fabric) of 0.75. This yarn offers new and novel fabrics that are especially valuable as sheeting.

EXAMPLE 16 Polyhexamethylene adipamide with a relative viscosity of 34 and containing 0.3% of TiO as a delustrant is extruded from a melt at a temperature of 287 C. through a spinneret at a temperature of 274 C. Each orifice of the spinner et consists of a 0.007 inch center hole with 6 slots 0.006 inch long by 0.003 inch Wide radiating outward at 60 angles from the circumference of the center hole.

Thirty-two of the orifices are arranged in rows with 6 and 7 orifices in alternate rows and orifices in adjacent rows being staggered. The orifices are located 0.050 inch apart on centers in a row and the rows are spaced 0.050 inch apart. Room temperature air at a rate of 1.5 s.c.f.m. is supplied through a ,4; inch by 3 inch slot directed to hit the threadline about 0.25 inch below the spinneret face. The quenching device is located one inch below the face of the spinneret and three inches away from the spinneret center line. The polymer is extruded at a rate of 0.208 gram per minute (12.9 'g./min./cm. and the yarn is collected and drawn with the feed rolls running at 620 y.p.m. and the draw rolls operating at 950 y.p.m. to give a draw ratio of 1.53X. The as-drawn yarn has a tenacity of 2.6 g.p.d., an elongation of 84%, and an initial modulus of 11.7 g.p.d.

The as-drawn yarn was then made into a tafieta fabric of plain weave with a finished fabric construction of 135 x 81 having a finished weight of 2.1 ounces per square yard, a bulk of 2.72 cmfi/ gram, and a coefficient of friction (fabric on fabric) of 0.66.

EXAMPLE 17 Polypropylene with a melt index of 0.7 (ASTM D-1238-57T) is extruded at a rate of 6.2 g./min./cm. from a pool of molten polymer at 280290 C. through the spinneret of Example 16 maintained at 260 C. and the yarn wound up at 170 y.p.m. A quenching nozzle with a Width of 1.25 inches and a height of 2 inches is placed with its long dimension vertical, /2 inch below the face of the spinneret and 1 inch horizontally distant from the outer row of filaments. Room temperature air is then fed through this nozzle at a rate of s.c.f.m. which affords a tension on the threadline of 30 mg. per denier.

The as-spun yarn (4.9 d.p.f.) is found to have a cross section very closely resembling the orifice shape. This is very unusual especially at such low deniers. After relaxation by boiling in water, the as-spun yarn has a tenacity of 2.0 g.p.d'. with a break elongation of 350%, an initial modulus of 7, and is crimped. The yarn can be drawn to increase its strength to 6 g.p.d. or higher.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

I claim:

1. A process comprising extruding a synthetic molten fiber-forming polymer through a plurality of orifices, said orifices forming a pattern in which the centers of the orifices are positioned at the corners of contiguous quadrilaterals formed by lines connecting the centers of adjacent orifices, each side of each quadrilateral being between about 0.005 and about 0.125 inch in length, all inside angles in each quadrilateral being at least 30, said polymer being extruded at the rate of at least 4 g./min./cm. of spinneret face area within the quadrilaterals, directing a stream of a quenching fluid against each filament at a velocity of at least O.6w +l50 feet per minute, wherein w is the rate of extrusion of the polymer in g./min./sq. cm. of effective spinneret face, within 1 inch of the spinneret face at an angle between below and 45 above the horizontal to cool the extruded filaments to a temperature below about 15 C. below the melting point of the polymer prior to a point 2 inches below the spinneret, the extruded filaments being under a tension of at least 0.003 gram per denier immediately below the spinneret.

2. The process of claim 1 in which the as-spun filaments have a tenacity of at least 0.8 g./d.

3. The process of claim 1 in which the quenching fluid is air.

4. The process of claim 1 in which the fiber-forming polymer is polyhexamethylene adipamide having a relative viscosity of at least 12.

5. The process of claim 1 in which the fiber-forming polymer is polyethylene terephthalate having a relative viscosity of at least 9.

6. The process of claim 1 in which the fiber-forming polymer is polypropylene.

7. The process of claim 1 in which all the quadrilaterals are similar.

8. The process of claim 1 in which the as-spun filaments are drawn sufiiciently to produce filaments, each of which has a denier of between 0.1 and about 1.0.

9. The process of claim 1 in which the fiber-forming polymer is extruded at a rate of at least 10 g./min./cm. of spinneret face area within the quadrilaterals.

10. The process of claim 9 in which the quenching fluid is air.

11. The process of claim 9 in which the fiber-forming polymer is polyhexamethylene adipamide having a relative viscosity of at least 12.

12. The process of claim 9 in which the fiber-forming polymer is polyethylene terephthalate having a relative viscosity of at least 9.

13. The process of claim 9 in which the fiber-forming polymer is polypropylene.

References Cited in the file of this patent UNITED STATES PATENTS 2,821,744 Spohn et a1. Feb. 4, 1958 

1. A PROCESS COMPRISING EXTRUDING A SYNTHETIC MOLTEN FIBER-FORMING POLYMER THROUGH A PLURALITY OF ORIFICES, SAID ORIFICES FORMING A PATTERN IN WHICH THE CENTERS OF THE ORIFICES ARE POSITIONED AT THE CORNERS OF CONTIGUOUS QUADRILATERALS FORMED BY LINES CONNECTING THE CENTERS OF ADJACENT ORIFICES, EACH SIDE OF EACH QUADRILATERAL BEING BETWEEN ABOUT 0.005 AND ABOUT 0.125 INCH IN LENGTH, ALL INSIDE ANGLES IN EACH QUADRILATERAL BEING AT LEAST 30*, SAID POLYMER BEING EXTRUDED AT THE RATE OF AT LEAST 4 G./MIN./CM.2 OF SPINNERET FACE AREA WITHIN THE QUADRILATERALS, DIRECTING A STREAM OF A QUENCHING FLUID AGAINST EACH FILAMENT AT A VELOCITY OF AT LEAST 0.6W2+150 FEET PER MINUTE, WHEREIN W IS THE RATE OF EXTRUSION OF THE POLYMER IN G./MIN./SQ. CM. OF EFFECTIVE SPINNERET FACE, WITHIN 1 INCH OF THE SPINNERET FACE AT AN ANGLE BETWEEN 45* BELOW AND 45* ABOVE THE HORIZONTAL TO COOL THE EXTRUDED FILAMENTS TO A TEMPERATURE BELOW ABOUT 15*C. BELOW THE MELTING POINT OF THE POLYMER PRIOR TO A POINT 2 INCHES BELOW THE SPINNERET, THE EXTRUDED FILAMENTS BEING UNDER A TENSION OF AT LEAST 0.003 GRAM PER DENIER IMMEDIATELY BELOW THE SPINNERET. 